3.2. Paleomagnetic Results
The samples were generally demagnetized up to 20 mT (for details, see
Supplementary Fig. S3), which removed the VRM component, causing a
change in the direction of remanent magnetization. This soft VRM
component has mean D: 13.8° and I: 56.8° values, which is close to the
present day Earth’s magnetic field direction for the Czech Republic (D:
4.4° and I: 66.8°) (see Supplementary Fig. S4). Some samples (01_8M,
04_2M, 17_2M, 17_9M, 22_0M) could not be demagnetized to 100 mT.
The intensity of the natural remanent magnetization (NRM) of the samples
varies between 8.5x10-3 and
34.1x10-3 A/m. Median destructive field (MDF) values,
where samples lost half of their magnetization, range between 5 and 8
mT. The NRM intensity and MDF values of the samples are shown in
Supplementary Fig. S4.
Fig. 6 shows the data in comparison with published studies, which
consisted of cave sediments (Bella et al., 2019; Ge et al., 2021; Shaar
et al., 2021; Muttoni et al., 2017), marine sediments (Liu et al., 2016;
Okada et al., 2017; Valet et al., 2014), and other types of sediments
(Giaccio et al., 2013; Sagnotti et al., 2014; Jin and Liu, 2011). The
MAD values for the Matuyama and Brunhes sections are between 0.3° and
5.4° (Fig. 6m). These values for the transition section are between 0.7°
and 5.3°, which is relatively reliable for detecting the migration of
the paleomagnetic vector from reversed to normal polarity (Fig. 6m). The
trend of the MAD values in our data increases before and during the
transition (shown with dashed lines and dots in Fig. 6m-o) between 23.1
and 7.1 cm depth. This increase can also be seen in other studies, while
these values are higher than those in our study (Fig. 6m-o).
Our paleomagnetic data showed inclination values that change by
approximately 90° (shown with empty and filled arrows
in Fig. 6e-h) from 12.8 to 7.1 cm depth (Fig. 6e). This result revealed
the transition nature of the Matuyama-Brunhes magnetic reversal in Za
Hajovnou cave. The change can be seen in other datasets from negative to
positive inclination (Fig. 6f-h). Between 12.8 and 11.8 cm depth,
inclination changes to a positive value (shown with circular arrows in
Fig. 6e-h) just before the transition in our data. Additionally, in
other studies, the change is larger in other types of sediments (Fig.
6h) than in cave and marine sediments (Fig. 6f and g). Below this depth,
the Matuyama section has inclination fluctuations (shown with dashed
lines in Fig. 6e-h) between -6.3° and
-89.3°. In other datasets (Fig. 6f-h), these
fluctuations are seen less frequently in other types of sediments (Fig.
6h). Above the transition, the inclination angle changes between
25.2° and 65.9° for the Brunhes
section in our data (Fig. 6 e).
Our declination data show more frequent fluctuations for the whole
sediment section (Fig. 6i). The change between 3.0 and 9.2 cm depth
(shown with empty and filled arrows in Fig. 6i-l) can be seen with a
larger difference in other studies. Below the transition, frequent
fluctuations (shown with dashed lines in Fig. 6i-l) with a large
declination change (shown with square arrows in Fig. 6i-l) between 25.3
and 23.1 cm depth were observed in other studies. These fluctuations in
cave sediments (Fig. 6j) are more frequent than in marine and other
types of sediments (Fig. 6k and l).
Despite the fluctuations,
the intensity values of ChRM, which can depend on the concentration
variation in magnetic carriers of every individual sample, decreased for
the Matuyama section from the bottom to the transition between 35.1 and
~15 cm depth in our data (Fig. 6d). After the transition
from reversed to normal polarity, these values increased in the Brunhes
section between 7.1 and 0 cm depth (Fig. 6d). Even though there are some
differences in absolute values due to the changes in the paleomagnetic
data depending on the location and sediment type, comparisons of this
dataset with other studies showed that fluctuations and frequency of
fluctuations in our data are consistent with other datasets and serve as
a supporting argument for the Matuyama-Brunhes magnetic reversal in Za
Hajovnou cave.